1. Field of the Invention
This invention relates to a plasma addressed liquid crystal display apparatus adapted for driving liquid crystal by making use of plasma to thereby display an image (pictorial image).
2. Background Art
As an image display apparatus for driving liquid crystal to carry out display of an image (pictorial image), a plasma addressed liquid crystal display apparatus utilizing discharge plasma is disclosed in the Japanese Patent Application Laid Open No. 265931/1992 publication, etc.
The proposed plasma addressed liquid crystal display apparatus comprises, as shown in FIG. 1, a liquid crystal side glass 12 having a plurality of electrodes 11 arranged in parallel to each other, a base (substrate) glass 14 having a plurality of discharge electrodes 13 arranged in parallel to each other and perpendicular to the electrodes 11, a thin glass plate 15 provided between the liquid crystal side glass 12 and the base glass 14, a liquid crystal layer 16 provided between the liquid crystal side glass 12 and the thin glass plate 15, a plurality of barrier ribs 18 formed on the discharge electrodes 13 within a discharge chamber 17 formed between the base glass 14 and the thin glass plate 15, and frit 19 provided so as to seal the discharge chamber 17.
The liquid crystal side glass 12 is flat and non-conductive, and sufficiently transparent from an optical point of view. A plurality of strip-shaped electrodes 11 are formed on one principal surface of the liquid crystal side glass 12, and a liquid crystal layer 16 comprised of nematic liquid crystal, etc. is disposed in a manner in contact with the electrodes 11. In particular, a plurality of the electrodes 11 formed with a predetermined width on the principal surface of the liquid crystal side glass 12 opposite to the base glass 14 are formed by transparent conductive material, e.g., indium tin oxide (ITO), etc., and are transparent from an optical point of view. In addition, these electrodes 11 are disposed in parallel to each other, and extend, e.g., in a vertical direction of the display screen.
The liquid crystal layer 16 is held between the thin glass plate 15 which is a thin dielectric plate and the liquid crystal side glass 12. A liquid crystal cell is formed by. By the liquid crystal side glass 12, the liquid crystal layer 16 and the thin plate glass 15. This thin glass plate 15 functions as an insulating shielding layer between the liquid crystal layer 16 and discharge chamber 17 which will be described later.
On the other hand, the base glass 14 on which a plurality of the discharge electrodes 13 are formed as a strip-shaped electrode and the thin glass plate 15 are adapted so that their peripheries are sealed by frit 19 as the sealing agent. In addition, a space formed between the base glass 14 and the thin glass plate 15 serves as the discharge chamber 17 for producing discharge plasma.
Respective discharge electrodes 13 are equi-distantly disposed on the base glass 14. Moreover, barrier ribs 18 respectively serving as barriers are formed on these discharge electrodes 13 by printing as described later. The discharge chamber 17 is partitioned by the plurality of barrier ribs 18 so that it is divided into respective plasma chambers P.sub.1, P.sub.2 . . . which form independent discharge channels, respectively.
The discharge electrodes 13 formed on the principal surface of the base glass 14 opposite to the liquid crystal side glass 12 are directly formed on the base glass 14 by a conductive paste including, e.g., silver powder, etc. The discharge electrodes 13 are also arranged in parallel to each other, wherein the arrangement direction thereof is the direction perpendicular to the electrodes 11 formed on the previously described liquid crystal side glass 12. Namely, these discharge electrodes 13 are arranged in a horizontal direction with respect to the display screen. Accordingly, respective plasma chambers P.sub.1, P.sub.2 . . . correspond to e.g., respective scanning lines within the display picture on screen. Ionizable gas is hermetically sealed into the respective plasma chambers P.sub.1, P.sub.2 . . . . As such ionizable gas, helium, neon, argon or mixture gas thereof is used.
Barrier ribs 18 are formed on the strip-shaped discharge electrodes 13 for every scanning unit. In particular, the barrier ribs 18 are formed by printing, plural times, in a stacked manner, using glass paste into which ceramic such as alumina, etc. is mixed by the printing method, e.g., the screen printing method, and also serves to limit the distance between the base glass 14 and the thin glass plate 15 (hereinafter referred to as the gap interval of the discharge chamber 17). The gap interval of the discharge chamber 17 can be controlled by adjusting the number of screen printing operations when forming the barrier ribs 18 or the quantity of glass paste at the time of each printing, etc. Ordinarily, the gap interval is to be about 200 .mu.m.
The discharge electrodes 13 function as the anode electrode or the cathode electrode, and discharge electrodes are constituted by pairing these electrodes. In the case where the barrier ribs 18 are formed on the discharge electrodes 13 as described above, each of the discharge electrodes 13 are commonly used for the two adjacent plasma chambers where the respective plasma chambers P.sub.1, P.sub.2 . . . are partitioned by these barrier ribs 18. Namely, e.g., the discharge electrode 13 between the plasma chamber P.sub.1 and the plasma chamber P.sub.2 serves as both the discharge electrode of the plasma chamber P.sub.1 and the discharge electrode of the plasma chamber P.sub.2.
A manufacturing process for the above-described plasma addressed liquid crystal display apparatus will be briefly described.
Initially, a plurality of discharge electrodes 13 are made on the glass base 14 by printing so that the barrier ribs 18 can then be stacked on these discharge electrodes 13 Further, frit 19 is coated at the periphery of the glass base 14 to form the discharge chamber 17. Thereafter, thin glass plate 15 is placed onto the upper portions of the barrier ribs 18 is vacuum evacuated the inside of the discharge chamber 17 is vaccum evacuated thereafter to inject gas thereinto.
The thickness of the thin glass plate 15 is about 50 .mu.m. The thin glass plate 15 functions an insulating shielding layer between the liquid crystal layer 16 and the discharge chamber 17 as described above. In the vacuum evacuating process and the gas injection process described above, as shown in FIG. 1, large stresses are applied to the portions indicated by Q.sub.1 and Q.sub.2 of the thin glass plate 15, i.e., the portions Q.sub.1 and Q.sub.2 at which the thin glass plate 15 is in contact with the edge portions of the barrier ribs 18. In addition, small cracks, so called micro cracks exist within glass.
Accordingly, in the above-described plasma addressed liquid crystal display apparatus, there was the problem that micro cracks at the portions Q.sub.1 and Q.sub.2 of the thin glass plate 15 become large by carrying out vacuum evacuation and injection of gas, so the thin glass plate 15 is cracked or broken.
In view of the actual circumstances as described above, an object of this invention is to provide a plasma addressed liquid crystal display apparatus capable of preventing the thin plate glass from being cracked or broken.